1. Field of the Invention
The present invention relates to a planar luminescent device used, for example, in backside illumination for a liquid crystal display panel.
2. Description of the Prior Art
As a prior art device of this type, one for example disclosed in Japanese Laid-open Utility Model Publication No. 62-69281 is known. This device is, as shown in FIG. 1, composed of a light transmitting plate 1, incandescent lamps 2a, 2b disposed on an end face of the light transmitting plate 1, a reflecting frame 3 enclosing the light transmitting plate 1 and the incandescent lamps 2a, 2b, and so on, in which emitted light from the incandescent lamps 2a, 2b is introduced into the light transmitting plate 1, scatteringly reflected by a scattering reflection layer (not shown) disposed on the back face of the light transmitting plate 1, and radiated from the surface of the light transmitting plate 1, whereby a liquid crystal display panel (not shown) or the like disposed in front of the light transmitting plate 1 is illuminated.
In such a prior art device, when for example an incandescent lamp 2a is disposed in such a way that the longitudinal direction of its filament 2aa lies in parallel with the end face 1a of the light transmitting plate 1, luminance distribution of the incandescent lamp 2a becomes as indicated by dotted line A in the drawing (it is thereby shown that light intensity is equal along the dotted line). Namely, the quantity of light incident on the end face 1a of the light transmitting plate 1 is larger at the portion close to the incandescent lamp 2a and smaller at the portion apart from it. As a result, the distribution of the quantity of the incident light becomes as indicated by dotted line B (it is thereby shown that light intensity is equal along the dotted line). Then, the radiated light from the surface of the light transmitting plate 1 becomes intense at the portion closer to the incandescent lamp 2a and it becomes weak at the portion away from the incandescent lamp 2a. Thus, there has been a problem that uniform planar luminous intensity cannot be obtained.